The present invention relates to a power tool, and more particularly to a high-speed power tool in which a tool is mounted on a housing for displacement relative thereto, and in which a motor drives the tool in oscillatory motion by a transmission including a crank member.
A wide variety of power tools in which the tool oscillates relative to the housing accommodating the driving motor is already known. Such tools usually utilize a crank member, such as an eccentric, for imparting oscillatory motion to the tool proper. Examples of power tools in which this concept is utilized are oscillating sanders, finishing or superfinishing tools, honing machines and similar devices. Depending on the intended use, the power tool may assume various configurations, and the tool element may also have different shapes. The invention will be presently discussed as utilized in a finishing tool, but it will be appreciated that the particular shapes of the power tool housing and of the tool element, as well as the uses to which the power tool is put may vary in a wide range.
Finishing tools of different constructions are already known. Basically, they may be classified as either low-speed finishing tools in which a finishing tool, such as a finishing plate, conducts 4 to 5 thousand oscillations per minute, and high-speed finishing tools in which the finishing plate conducts 6,000 or more oscillations per minute. High-speed finishing tools have smaller amplitudes of oscillation than low-speed finishing tools, which results in a better quality of the finished surface.
While the finishing plate of any of the heretofore known low-speed finishing tools is driven by the motor via a transmission interposed between the output shaft of the motor and the crank member, some of the high-speed finishing tools have the crank member driven by a transmission, while other high-speed finishing tools employ the motor to directly drive the crank member or even have the output shaft shaped as a crank shaft. In the latter case, the finishing tool has a particularly simple construction; on the other hand, however, this construction is also disadvantageous in that the driving motor utilized therein has considerable dimensions and weight.
All high-speed finishing tools have a drawback that a bearing which transmits the orbiting movement of the eccentric portion of the crank member to the finishing tool plate, has a significantly reduced lifespan as compared to a similar bearing utilized in a low-speed finishing tool. The lifespan of this bearing is dependent only on the speed of oscillation of the finishing plate, and is independent of the fact whether or not a transmission is interposed between the crank member and the driving motor.
The prior art high-speed finishing tools of this type have the drawback that it is very difficult to exchange a worn-out bearing interposed between the eccentric part of the crank member and the finishing plate. This is partially attributable to the fact that, when the bearing is to be exchanged, adhesively connected sealing locations are to be separated and then, when the new bearing is installed, these sealing locations have to be adhesively connected again. These operations are rather laborious and time-consuming, and can only be performed by skilled personnel using special tools and devices.